| HS Code | 707559 |
| Product Name | Xinjiang Zhongtai Chemical Caustic Soda Flakes |
| Chemical Name | Sodium hydroxide |
| Chemical Formula | NaOH |
| Cas Number | 1310-73-2 |
| Molecular Weight | 40.00 g/mol |
| Appearance | White translucent flakes |
| Purity | 99.0% min |
| Grade | Industrial grade |
| Density | 2.13 g/cm3 at 20°C |
| Melting Point | 318°C |
| Boiling Point | 1388°C |
| Solubility In Water | Highly soluble, exothermic |
| Ph | 14 (1% solution) |
| Odor | Odorless |
| Hygroscopicity | Hygroscopic, absorbs moisture and CO2 from air |
As an accredited Xinjiang Zhongtai Chemical Caustic Soda Flakes factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Xinjiang Zhongtai Chemical Caustic Soda Flakes are packed in 25 kg PP woven bags with PE liner, 40 bags per pallet. |
| Container Loading (20′ FCL) | 20′ FCL: caustic soda flakes packed in 25kg PP/PE bags, palletized, loaded, and secured for safe transport. |
| Shipping | Shipping caustic soda flakes from Xinjiang Zhongtai requires secure packaging in 25kg PP/PE woven bags, palletized and containerized for sea freight. Classified as UN1823, Class 8 corrosive, it must be kept dry and away from moisture. Standard shipment is approximately 20–25 MT per 20ft container, with proper hazmat documentation. |
| Storage | Store caustic soda flakes in a cool, dry, well-ventilated warehouse, away from moisture, water, acids, and incompatible chemicals. Keep containers tightly sealed and elevated on pallets to prevent dampness. Protect from direct sunlight and physical damage. Ensure spill containment measures and emergency eyewash/shower access are available. |
| Shelf Life | Store in airtight, dry conditions; shelf life is approximately two years from date of manufacture. |
Caustic soda flakes supplied by Xinjiang Zhongtai Chemical are released to downstream industrial users as deliquescent white solids, typically evaluated against GB/T 209-2018 for sodium hydroxide solid grades. The material is produced with a minimum NaOH content of 99.0 wt% on a dry basis, with controlled carbonate, chloride, and iron residues. Dissolution in water at 20–25 °C liberates more than 1,000 kJ/kg of heat; therefore, make-down vessels are specified with cooling coils or external recirculation when the target solution strength exceeds 10 wt%. At relative humidity above 60%, the flakes absorb atmospheric moisture and cake in storage silos and feed hoppers, so hopper outlets are specified with a 60° cone angle and low-humidity purge air. The material is incompatible with aluminium, zinc, tin, and acid-generating chemicals; dry contact with chlorinated organic solvents is excluded from operational handling. The downstream applications covered here are restricted to established industrial processes in which sodium hydroxide acts as a reaction reagent, pH buffer, or extraction agent.
Across Bayer-circuit alumina refineries, caustic concentration in the pregnant liquor controls bauxite extraction efficiency, desilication product formation, and precipitation yield. Incoming flake caustic from Xinjiang Zhongtai Chemical is dissolved in weak wash water or spent liquor to raise the Na₂Oₐ titre before injection into the digestion loop. The prevailing procurement standard is GB/T 209-2018 solid sodium hydroxide grade IS-IT I, cross-checked against site-specific impurity limits for chloride, carbonate, and iron because carbonate and organic impurities contribute to oxalate scale in heat exchangers and precipitation vessels. Smelting-grade alumina operations also maintain quality plans under ISO 9001:2015 and environmental permits under ISO 14001:2015. The addition ratio is expressed not as a single dosage but as the digestion liquor molar ratio of caustic to alumina. For diasporic bauxite processed at 240–270 °C, mills maintain a molar ratio from 1.45 to 1.65, corresponding to circulating caustic concentrations of 200–260 g/L Na₂Oₐ. Beneath 1.40, boehmitic ore extraction can fall below 80%, leaving recoverable alumina in red mud; above 1.70, quartz dissolution accelerates and sodalite or cancrinite scale reduces heat-transfer coefficients in flash coolers and tubular heaters. Downstream processing includes bauxite grinding in ball mills or rod mills, predesilication at 90–105 °C, high-pressure digestion in multi-chamber autoclaves or tube digesters with live steam heating, flash cooling to atmospheric pressure, red mud separation in thickeners and counter-current washers, security filtration of the pregnant liquor, and seeded precipitation in mechanically agitated precipitators. The crystalline product is classified as smelter-grade alumina Al₂O₃; hydrate fractions are diverted to non-metallurgical uses such as flame retardants and ceramics, and red mud is disposed in engineered impoundments. Published inter-refinery caustic-loss data for this specific configuration are limited because bauxite mineralogy and organic carbon load vary by deposit, but the operating window around molar ratio and temperature is well documented.
Kraft pulp mills use flake caustic for recausticising loop correction and oxidative extraction alkali, but the addition point is more constrained than in simple neutralisation. Compliance for the pulping line is derived from the EU Industrial Emissions Directive 2010/75/EU BAT conclusions for pulp and paper; North American mills operate under US EPA Cluster Rule 40 CFR Part 430, and where bleached board is intended for food-contact packaging, the converter verifies compliance with 21 CFR 176.170 and 21 CFR 176.180. Addition ratios in the digester are calculated as effective alkali charge on oven-dry wood. Softwood kraft pulping typically operates between 15% and 22% effective alkali as Na₂O, with sulfidity held between 25% and 35%. Flake caustic is added to the causticiser to maintain causticising efficiency at 80–85%, meaning that the sodium carbonate in recirculated weak liquor is converted to hydroxide before white liquor returns to the digester. In the oxidative extraction stage of a bleach sequence, sodium hydroxide is dosed at 1.0–2.5 wt% on oven-dry pulp, typically in an Eop or Ep stage with oxygen pressurisation above 0.3 MPa. The downstream process includes chip steaming and impregnation, continuous cooking in a hydraulic digester at 145–170 °C for softwood or batch digesters for sawdust and short-fibre furnishes, brownstock washing in diffusers or twin-roll presses, oxygen delignification in medium-consistency reactors, and bleaching in upflow towers. Flake caustic is made down in a weakly caustic dissolving tank at 20–25 wt% before metering into the recausticising loop or the bleach plant alkali header. Terminal outputs are unbleached kraft pulp, bleached softwood kraft, linerboard, sack kraft, and dissolving pulp for viscose or lyocell production. The main process boundary is overdosing in oxidative extraction: above 3.0 wt% NaOH on pulp, cellulose peeling reactions lower intrinsic viscosity below 500 dm³/kg in dissolving grades, which is measured by ISO 5351:2010 or equivalent.
Mercerising range performance depends on caustic concentration as a function of dwell time and fabric tension, and the operation is conducted on a chain merceriser or pad-batch line rather than as a simple aqueous dip. Compliance in the textile supply chain is managed under ZDHC MRSL V3.1, REACH EC 1907/2006, and Oeko-Tex Standard 100 where finished fabric is certified; discharge permits for the caustic recovery train require that at least 85% of the wash liquor is recovered or neutralised before release. The working bath for fabric mercerisation is maintained at 220–300 g/L NaOH, equivalent to 18–24 °Bé, while pad-batch scouring of greige cotton may use 150–200 g/L. Cold causticising of cellulosic knitwear operates at 160–220 g/L, with a cresol-free mercerising wetting agent dosed at 0.3–1.0 g/L. Downstream processing requires dry fabric to enter the saturator under low tension; dwell time after impregnation is 30–60 seconds at 15–25 °C. The web is stretched by tenter clips or driven roll nips to prevent shrinkage, then washed in a multi-stage counterflow recovery train with boiling water to strip the alkali before acid neutralisation. Terminal products include high-gloss cotton poplin, dimensional-stable shirting, cotton/linen blends, and mercerised cotton yarn for knitwear. The process window is narrow: caustic concentration below 200 g/L at ambient temperature produces incomplete swelling, dull surface, and uneven dye uptake; above 320 g/L, the fibre can tender if tension control is lost. Recovery limitations are important because dilute wash streams below 30 g/L NaOH are usually uneconomical to re-concentrate by evaporation.
For full-boiled soap kettles, the sodium hydroxide flake addition is matched to the measured saponification value of the fat charge, not to a fixed recipe mass. Compliance for detergent soap is governed by EU Detergents Regulation (EC) No 648/2004 for finished product labelling, REACH EC 1907/2006 for sodium hydroxide registration, and EC 1223/2009 when soap is marketed with cosmetic claims; occupational exposure limits under national implementations of EU Directive 98/24/EC also apply to the caustic make-down area. The theoretical sodium hydroxide demand is calculated from the saponification value using the factor 0.713 by which KOH equivalents are converted to NaOH equivalents; a fat with a saponification value of 200 mg KOH/g requires 142.6 g NaOH per 1 kg oil. Commercial full-boiled charges therefore add 12–15 wt% NaOH on oil weight as a 25–30 wt% solution. Finished soap retains free caustic below 0.05 wt% to avoid skin irritation and bar cracking. The downstream process uses full-boiled kettles with open or closed steam coils; fat is charged and heated to 80–100 °C, and caustic solution is metered gradually to avoid soap-phase inversion. Brine or dry salt is added after saponification to grain the neat soap and separate glycerine in the spent lye; the soap is then washed, settled, and processed through vacuum spray dryers or roll mills and plodders into bars. Terminal products include toilet soap bars, laundry soap bars, soap noodles for downstream extrusion, and translucent soap formulations. The main operational limit is free caustic above 0.1 wt% in neat soap, which produces brittle bars, darkens colour through oxidation, and may initiate rancidity; under-alkali charges leave unsaponified fat and reduce bar hardness.
Water-based drilling fluid systems use sodium hydroxide to control pH, precipitate divalent cations, and suppress the conversion of caustic to bicarbonate in high-CO₂ drilling environments. Compliance for the additive is set by API Spec 13A and ISO 13500:2008 for drilling fluid materials; caustic soda may be procured against ANSI/AWWA B501-19 or GB/T 209-2018 depending on the regional supply chain. Addition ratios are field-tested with a pH titration, because the required caustic concentration depends on native alkalinity, bentonite concentration, and drilled-gas carbonate loading. Typical additions range from 0.25 lb/bbl to 1.5 lb/bbl (0.7–4.3 kg/m³) to maintain bulk pH in the 9.5–11.0 window. Seawater muds may require an initial caustic sweep to precipitate magnesium before full bentonite hydration; the flake is pre-dissolved in a mixing barrel to 10–20 wt% NaOH and metered into the suction pit ahead of the mud hopper and shale shaker discharge. Downstream processing includes the continuous circulation of the fluid through the pit, centrifugal pump, drill pipe, bit nozzles, annulus, and solids-control equipment; pH is monitored with glass electrodes and maintained below 12.0 to avoid degradation of xanthan gum and other biopolymers. Terminal product is water-based drilling fluid used in vertical and directional wells; spent mud and cuttings are disposed under local waste permits. The operational boundary is direct dry feeding into the active mud pit, which is avoided because localised high-pH regions flocculate bentonite and destroy polymer viscosity; total carbonate/bicarbonate alkalinity above 20,000 mg/L is also a known cause of rheological instability in reactive shale intervals.
Caustic soda flake is made down to a working solution and dosed against a pH setpoint in continuous neutralisation of acidic metal-bearing effluent, with residence time and mixing energy as controlling variables. Compliance for potable water treatment chemicals is often based on ANSI/AWWA B501-19 or EN 896:2012 where national approvals apply, while industrial effluent discharge is regulated by site permits under the EU Industrial Emissions Directive 2010/75/EU or US 40 CFR Part 403 pretreatment standards. Stoichiometric addition ratios derive from the equivalent weight of sodium hydroxide: 40.0 g NaOH neutralises 36.5 g HCl, and 80.0 g NaOH neutralises 98.1 g H₂SO₄; for phosphoric acid neutralisation to trisodium phosphate, 120.0 g NaOH neutralises 98.0 g H₃PO₄. Working solutions are prepared at 5–10 wt% NaOH to reduce freezing risk and to limit the temperature rise in the make-down tank. Downstream treatment uses a sequenced dissolution tank with a 304L or 316L stainless steel agitator; the solution is injected into a flash mixer or in-line static mixer ahead of a neutralisation reactor, with pH controlled between 6.0 and 9.0 before flocculation and lamella clarification. Terminal outputs are neutralised discharge water for municipal sewer release, metal hydroxide sludge from precipitation, and recycled process water after filtration. The main limitation is overdosing in aluminium-bearing wastewater above pH 9.5, because amphoteric aluminium hydroxide redissolves and increases residual metal concentration. Direct dry feeding into acidic tanks is excluded due to thermoshock and uncontrolled carbon dioxide stripping.
| Acid or acidic stream | Sodium hydroxide demand per unit acid mass at 25 °C |
|---|---|
| Hydrochloric acid, HCl | 1.097 kg 100% NaOH basis per 1.0 kg HCl |
| Sulfuric acid, H₂SO₄ | 0.816 kg 100% NaOH basis per 1.0 kg H₂SO₄ |
| Phosphoric acid, H₃PO₄, to trisodium phosphate | 1.225 kg 100% NaOH basis per 1.0 kg H₃PO₄ |
Competitive Xinjiang Zhongtai Chemical Caustic Soda Flakes prices that fit your budget—flexible terms and customized quotes for every order.
For samples, pricing, or more information, please contact us at +8615365186327 or mail to sales3@liwei-chem.com.
We will respond to you as soon as possible.
Tel: +8615365186327
Email: sales3@liwei-chem.com
Flexible payment, competitive price, premium service - Inquire now!
Xinjiang Zhongtai Chemical caustic soda flakes are manufactured by ion-exchange membrane chlor-alkali electrolysis, followed by evaporation, flaking, and cooling. The product is designated as solid sodium hydroxide, flake form, premium grade IS under GB/T 209-2018, and the typical certificate of analysis reports sodium hydroxide mass fraction ≥99.0 wt%, sodium carbonate ≤0.5 wt%, sodium chloride ≤0.03 wt%, and iron oxide ≤0.001 wt%. The flake is white, deliquescent, and strongly alkaline, with molecular weight 40.00 g/mol, melting point 318°C, boiling point 1390°C, and water solubility of approximately 111 g/100 mL at 20°C. Loose bulk density is approximately 0.9–1.2 g/cm³, depending on flake thickness and screening. The material is classified as corrosive solid under UN 1823, hazard class 8, packing group II, and is commonly packed in 25 kg multi-wall bags with an inner polyethylene liner. Because the production route is membrane-cell based, the flakes do not contain process mercury; chloride and chlorate residuals are lower than those associated with diaphragm-cell solid caustic.
The dissolving behavior is central to equipment specification. When sodium hydroxide dissolves, the enthalpy of solution at infinite dilution is approximately -44.5 kJ/mol, which means that preparing a 25 wt% caustic solution from 20°C water can produce a calculated adiabatic temperature rise of roughly 65°C. Production-scale dissolution therefore uses jacketed 316L stainless steel or nickel-alloy vessels with turbine agitation, and the caustic is added to water under controlled feed rather than water to caustic. Demineralized or soft water is preferred because calcium and magnesium ions form insoluble hydroxide precipitates and scale.
The critical impurity boundaries for the premium flake grade are sodium chloride, sodium carbonate, and iron oxide. Sodium chloride in membrane-cell caustic originates mainly from incomplete rejection of chloride by the ion-exchange membrane; the limit of ≤0.03 wt% is a function of membrane selectivity, catholyte concentration control, and evaporator feed quality. Sodium carbonate forms during contact with atmospheric carbon dioxide in evaporation, flaking, packaging, and storage; the ≤0.5 wt% limit is an operational boundary that requires minimizing exposure to humid air and keeping packaging sealed. Iron oxide at ≤0.001 wt% is controlled by the choice of corrosion-resistant evaporator and flaker metallurgy, and is relevant for dissolving pulp, rayon, and high-purity alumina where iron discoloration or catalytic effects are undesirable.
In comparison with diaphragm-cell solid caustic, the membrane-grade flake carries lower sodium chloride and sodium chlorate because the polymer diaphragm permits more brine leakage than a functioning perfluorinated membrane. Mercury-cell caustic, while often low in chloride, introduces mercury containment and analytical control requirements not present in membrane-cell material. Within the same national standard, premium grade IS differs from first-class IT and qualified II mainly in the maximum impurity tolerances shown in the comparative table below. Where downstream equipment includes stressed 316L or duplex stainless steel in hot caustic service, chloride carry-in is a recognized contributor to chloride stress corrosion cracking; published data for specific customer-specific corrosion rates is limited, but the substitution of lower-chloride membrane-grade caustic is generally made to reduce that risk.
| Parameter | Premium grade IS | Normative reference |
|---|---|---|
| Sodium hydroxide mass fraction | ≥99.0 wt% | GB/T 209-2018 |
| Sodium carbonate mass fraction | ≤0.5 wt% | GB/T 209-2018 |
| Sodium chloride mass fraction | ≤0.03 wt% | GB/T 209-2018 |
| Iron oxide mass fraction | ≤0.001 wt% | GB/T 209-2018 |
| Parameter | Premium grade IS | First class IT | Qualified II |
|---|---|---|---|
| NaOH mass fraction | ≥99.0 wt% | ≥98.5 wt% | ≥98.0 wt% |
| Na₂CO₃ mass fraction | ≤0.5 wt% | ≤0.8 wt% | ≤1.0 wt% |
| NaCl mass fraction | ≤0.03 wt% | ≤0.05 wt% | ≤0.07 wt% |
| Fe₂O₃ mass fraction | ≤0.001 wt% | ≤0.003 wt% | ≤0.005 wt% |
In alumina refinery digestion circuits, the flake is dissolved into Bayer liquor to compensate for sodium hydroxide consumed in bauxite digestion and red mud washing. Process temperatures are ore-specific: gibbsitic bauxite digestion is typically carried out near 100–150°C, boehmitic digestion near 200–250°C, and diasporic bauxite may require higher temperatures with lime addition. Caustic concentration is managed as a function of the alumina-to-caustic ratio, with refinery operators controlling the blow-off liquor concentration, the digestion liquor charge, and the red mud circuit wash water balance. Because the flake is fed as a solid, high-pressure tube digesters and agitated autoclaves require reliable flake dissolution and filtering upstream to prevent undissolved solids or packaging fragments from entering the Bayer circuit.
In chemical pulp processing, the caustic flake is dissolved for oxygen delignification and extraction bleaching at approximately 8–12 wt% NaOH on oven-dry pulp, and for mercerizing at 17–25 wt% NaOH. Mercerizing is typically conducted at 15–18°C to improve cotton fiber swelling and luster. Low iron content is critical in these uses because precipitated iron oxide can stain cellulosic fibers and reduce brightness. In viscose staple and filament manufacture, steeping lye at about 18–20 wt% NaOH is used to convert cellulose to alkali cellulose; high chloride or iron load can affect press cake separation, filterability, and final product color. The low impurity profile of membrane-grade flakes supports these applications when the material is dissolved into demineralized water and filtered through a fine screen before use.
In soap and detergent saponification, sodium hydroxide is added according to the saponification value of the fat or oil charge; the flake product allows formulation of concentrated caustic without shipping water but requires fat/oil mixing temperature control because the saponification reaction is also exothermic. In petroleum refining, caustic is used in sweetening and in the removal of hydrogen sulfide and mercaptans; spent caustic disposal or regeneration is required, and sodium carbonate content can contribute to scaling in scrubber internals. In neutralization of acid waste streams, the product is added as a prepared solution of known normality, with pH control and alkalinity monitoring used to prevent pH overshoot. The product is not automatically food-grade or pharmaceutical-grade; those applications require separate qualification against the relevant compendial or food additive standards.
In industrial water treatment, caustic solution is injected into recirculating cooling water or boiler feed to adjust pH and regenerate demineralizer anion exchangers. Regeneration of strong-base anion resin uses 4–8 wt% NaOH, and hardness-free dilution water is required to avoid fouling the resin with calcium and magnesium hydroxide. In acid waste neutralization, flake-based caustic is often diluted to 20–25 wt% before injection to reduce freezing and improve pump compatibility; pH control loops with a final trim zone are used to avoid precipitation of dissolved metals at high local pH.
Substituting the flake product for 50 wt% liquid caustic shifts the logistical and engineering burden from liquid storage and freeze management to solid feeding and dissolution exotherm. A 50 wt% liquid caustic solution freezes near 12°C, so tanks, transfer lines, and pump heads in cold climates require heat tracing and insulation. Flake eliminates that freeze point but requires a dry solids feeder, a dissolution tank with controlled water addition, and cooling capacity. Because the dissolution enthalpy of NaOH is approximately -44.5 kJ/mol, direct preparation of 50 wt% solution from flakes and ambient water can generate local boiling and spattering. Therefore, the dissolving tank is normally designed with an external recirculation loop through a heat exchanger, or with jacket cooling, and the flake feed rate is interlocked with the tank temperature and caustic concentration.
Compared with liquid caustic, flake reduces shipment mass per dry alkali unit by eliminating approximately 50 wt% water, but it also introduces dust and caking hazards if the solid is exposed to humid air. Compared with prilled caustic, flakes dissolve faster due to higher specific surface area, but they can compact more readily in silos and should not be stored in deep piles above the design loading of the feeder. High-concentration caustic solutions prepared from flakes should be stored in 316L stainless steel, nickel-alloy, or lined carbon steel; unlined carbon steel may suffer excessive alkaline attack under stagnant high-temperature conditions. Published data for specific tank life in end-user facilities is limited because corrosion rates depend on temperature, stress, chloride, and flow velocity; therefore materials selection is based on recognized corrosion-test standards and caustic service guidelines rather than a single universal lifespan.
Flake thickness is controlled by flaker speed and knife clearance. Thicker flakes reduce dusting but dissolve more slowly in weak agitation, while thinner flakes improve dissolution rate at the cost of higher dust potential. Batch-to-batch variation is reported on the certificate of analysis and normally remains well within the standard limits, but humid storage can shift carbonate values upward over time. Compared with caustic soda pearls, the flake form may exhibit faster lye make-up at 20–40°C, but it is more sensitive to open-bag moisture pickup and should be consumed promptly after opening.
Moisture ingress is the dominant storage failure mode. At relative humidity above approximately 40%, the flake surface begins to absorb water; above 60% RH, surface dissolution can create a liquid film that combines flakes into a hard cake and bridges screw feeders, rotary valves, and silo outlets. Dry-air purging with a dew point below -20°C and sealed bag handling are used to maintain free flow. Storage at temperatures above 40°C increases water and carbon dioxide uptake, gradually raising surface carbonate content and potentially moving the bulk Na₂CO₃ value above the ≤0.5 wt% premium grade limit if bags remain open.
The product is corrosive to aluminum, zinc, tin, and magnesium and is incompatible with acids, ammonium salts, cyanides, and reactive organic compounds. Contact with amphoteric metals liberates hydrogen, so closed vessels and hoppers must be vented and purged where metal contact is possible. Operator exposure during flake transfer, dissolving, and cleaning requires liquid-tight chemical protection: gloves conforming to EN 374, eye protection conforming to EN 166, and respiratory protection where dust may be generated. Spill management involves dry collection to avoid creating a large exothermic liquid pool, followed by thorough water rinsing only after incompatible materials are removed. Storage beyond 12 months is not recommended because of progressive moisture and carbon dioxide pickup, and inventory should be rotated on a first-in, first-out basis.
Committed to quality, innovation, and reliable chemical solutions for a sustainable future.
